Morphometric analysis of lungfish endocasts elucidates early dipnoan palaeoneurological evolution
The lobe-finned fish, lungfish (Dipnoi, Sarcoptergii), have persisted for ~400 million years from the Devonian Period to present day. The evolution of their dermal skull and dentition is relatively well understood, but this is not the case for the central nervous system. While the brain has poor pre...
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| Format: | Article |
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eLife Sciences Publications Ltd
2022-07-01
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| Series: | eLife |
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| Online Access: | https://elifesciences.org/articles/73461 |
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| author | Alice M Clement Tom J Challands Richard Cloutier Laurent Houle Per E Ahlberg Shaun P Collin John A Long |
| author_facet | Alice M Clement Tom J Challands Richard Cloutier Laurent Houle Per E Ahlberg Shaun P Collin John A Long |
| author_sort | Alice M Clement |
| collection | DOAJ |
| description | The lobe-finned fish, lungfish (Dipnoi, Sarcoptergii), have persisted for ~400 million years from the Devonian Period to present day. The evolution of their dermal skull and dentition is relatively well understood, but this is not the case for the central nervous system. While the brain has poor preservation potential and is not currently known in any fossil lungfish, substantial indirect information about it and associated structures (e.g. labyrinths) can be obtained from the cranial endocast. However, before the recent development of X-ray tomography as a palaeontological tool, these endocasts could not be studied non-destructively, and few detailed studies were undertaken. Here, we describe and illustrate the endocasts of six Palaeozoic lungfish from tomographic scans. We combine these with six previously described digital lungfish endocasts (4 fossil and 2 recent taxa) into a 12-taxon dataset for multivariate morphometric analysis using 17 variables. We find that the olfactory region is more highly plastic than the hindbrain, and undergoes significant elongation in several taxa. Further, while the semicircular canals covary as an integrated module, the utriculus and sacculus vary independently of each other. Functional interpretation suggests that olfaction has remained a dominant sense throughout lungfish evolution, and changes in the labyrinth may potentially reflect a change from nektonic to near-shore environmental niches. Phylogenetic implications show that endocranial form fails to support monophyly of the ‘chirodipterids’. Those with elongated crania similarly fail to form a distinct clade, suggesting these two paraphyletic groups have converged towards either head elongation or truncation driven by non-phylogenetic constraints. |
| first_indexed | 2024-04-12T02:54:41Z |
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| institution | Directory Open Access Journal |
| issn | 2050-084X |
| language | English |
| last_indexed | 2024-04-12T02:54:41Z |
| publishDate | 2022-07-01 |
| publisher | eLife Sciences Publications Ltd |
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| series | eLife |
| spelling | doaj.art-fe0fbc43c02249cabc36f012098fb7b42022-12-22T03:50:52ZengeLife Sciences Publications LtdeLife2050-084X2022-07-011110.7554/eLife.73461Morphometric analysis of lungfish endocasts elucidates early dipnoan palaeoneurological evolutionAlice M Clement0https://orcid.org/0000-0003-0380-7347Tom J Challands1Richard Cloutier2Laurent Houle3Per E Ahlberg4https://orcid.org/0000-0001-9054-2900Shaun P Collin5John A Long6https://orcid.org/0000-0001-8012-0114College of Science and Engineering, Flinders University, Adelaide, AustraliaSchool of Geosciences, University of Edinburgh, Edinburgh, United KingdomDépartement de Biologie, Chimie et Géographie, Université du Québec à Rimouski, Rimouski, CanadaDépartement de Biologie, Chimie et Géographie, Université du Québec à Rimouski, Rimouski, CanadaSubdepartment of Evolution and Development, Department of Organismal Biology, Uppsala University, Uppsala, SwedenSchool of Life Sciences, La Trobe University, Melbourne, AustraliaCollege of Science and Engineering, Flinders University, Adelaide, AustraliaThe lobe-finned fish, lungfish (Dipnoi, Sarcoptergii), have persisted for ~400 million years from the Devonian Period to present day. The evolution of their dermal skull and dentition is relatively well understood, but this is not the case for the central nervous system. While the brain has poor preservation potential and is not currently known in any fossil lungfish, substantial indirect information about it and associated structures (e.g. labyrinths) can be obtained from the cranial endocast. However, before the recent development of X-ray tomography as a palaeontological tool, these endocasts could not be studied non-destructively, and few detailed studies were undertaken. Here, we describe and illustrate the endocasts of six Palaeozoic lungfish from tomographic scans. We combine these with six previously described digital lungfish endocasts (4 fossil and 2 recent taxa) into a 12-taxon dataset for multivariate morphometric analysis using 17 variables. We find that the olfactory region is more highly plastic than the hindbrain, and undergoes significant elongation in several taxa. Further, while the semicircular canals covary as an integrated module, the utriculus and sacculus vary independently of each other. Functional interpretation suggests that olfaction has remained a dominant sense throughout lungfish evolution, and changes in the labyrinth may potentially reflect a change from nektonic to near-shore environmental niches. Phylogenetic implications show that endocranial form fails to support monophyly of the ‘chirodipterids’. Those with elongated crania similarly fail to form a distinct clade, suggesting these two paraphyletic groups have converged towards either head elongation or truncation driven by non-phylogenetic constraints.https://elifesciences.org/articles/73461dipnoiendocasttomographypalaeoneurologypalaeozoicPCA |
| spellingShingle | Alice M Clement Tom J Challands Richard Cloutier Laurent Houle Per E Ahlberg Shaun P Collin John A Long Morphometric analysis of lungfish endocasts elucidates early dipnoan palaeoneurological evolution eLife dipnoi endocast tomography palaeoneurology palaeozoic PCA |
| title | Morphometric analysis of lungfish endocasts elucidates early dipnoan palaeoneurological evolution |
| title_full | Morphometric analysis of lungfish endocasts elucidates early dipnoan palaeoneurological evolution |
| title_fullStr | Morphometric analysis of lungfish endocasts elucidates early dipnoan palaeoneurological evolution |
| title_full_unstemmed | Morphometric analysis of lungfish endocasts elucidates early dipnoan palaeoneurological evolution |
| title_short | Morphometric analysis of lungfish endocasts elucidates early dipnoan palaeoneurological evolution |
| title_sort | morphometric analysis of lungfish endocasts elucidates early dipnoan palaeoneurological evolution |
| topic | dipnoi endocast tomography palaeoneurology palaeozoic PCA |
| url | https://elifesciences.org/articles/73461 |
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